IO controllers provide a connection between a computer operating system and an IO interface. Conventional operating systems create descriptor lists that form the instructions that an IO controller reads and follows in order to do its work. Current implementations of IO controllers include hardware circuits which read and initiate the operations defined in the descriptors. Any significant variation in the descriptor requires a new circuit, consequently rendering existing circuits obsolete. In practice, this creates the situation in which the development of new operating systems and the development of new hardware is delayed because the development of either requires coordination with the other.
The operational speed of an IO controller interface is typically fixed and the controller is limited to the bandwidth of the interface. The addition of another interface requires the addition of an add-on board or the redesign of a motherboard to accommodate a new controller interface device.
Attempts to increase the bandwidth of an IO device have required modification of the device hardware, precluding the dynamic addition of bandwidth. Modification or addition of hardware to a system has numerous disadvantages including reconfiguration expense, additional hardware expense and possible incompatibility with an existing operating system. Further, the addition of new hardware is performed while a system is turned off, requires a technician to install new hardware, and possibly requires a system administrator to change the operating system to support the new hardware. This process can be difficult, error prone and require expensive, time consuming design and re-qualification.
It is therefore desirable to have a device capable of accommodating the variation of a descriptor to add features, improve performance or provide forward or backward compatibility. Additionally, it is desirable to have a device which can be adapted to provide additional bandwidth by dynamically creating new instance of the IO controller in response to the requirements of a system without the addition of new hardware.